1. Field of the Invention
This invention relates to a process for the preparation of silver halide photographic light-sensitive materials. More particularly, this invention relates to a method of drying a layer of silver halide emulsion(s) coated on a support in the preparation of the silver halide photographic light-sensitive materials.
2. Description of the Prior Art
Generally stated, the preparation of silver halide photographic light-sensitive materials is accomplished by the steps of: preparing a silver halide emulsion(s); adding additives such as film hardeners, coating assistants and the like thereto; coating the same on a flexible lengthy support (hereinafter referred to as a "web"); cooling, setting, drying and further humidifying the same. In this case, more than two layers of silver halide emulsions are often coated, and, in addition, such emulsions are sometimes coated along with an auxiliary layer such as a protective layer or a backing layer.
The customary manner of drying the layers of silver halide emulsions on the support as described above has been to blow air at a temperature of from 20.degree. to 40.degree. C. and at a relative humidity of from 15 to 60% against the silver halide emulsion(s) layer(s) on the web at an air velocity of 15 to 30 m/sec so as to dry them as slowly as possible (hereinafter referred to as "air drying"). While other gases could be used, on a commercial scale air is the universal choice. The air drying is usually completed in about 3 to about 10 minutes.
These conditions are usually utilized for the initial drying step of the present invention, but the initial drying step of the present invention, but the initial drying step is completed shorter than the air drying of the prior art, usually about 50% to about 70% of the prior art.
In the step of making silver halide photographic materials, it is advantageous to carry out coating in a continuous manner, and, therefore, coating is usually carried out without interruptions by supplying a web, which is in the form of a butt-joined strip obtained by successively splicing limited lengths of webs to each other by butt-splicing or the like, to a coating station. It appears, however, that when a coating liquid having fluidity is applied to such spliced portions of a web by a continuous operation, several significant defects occur, principally downstream of the spliced portions. One defect is that air bubbles are introduced between the web surface and the coating layer directly after spliced portions, and air bubbles adhere to a coating nozzle, resulting in undesirable phenomena such as longitudinal stripes on the film surface coated over a considerable length. Another defect is that because of the occurrence of step-wise discontinuous variations at the trailing edge of the joining tape at the spliced portion (and due to the presence of the aforesaid air bubbles), the film coated on the web surface forms uncoated air bubbles), the film coated on the web surface forms uncoated portions, excessively thinly coated portions and locally thickly coated portions directly after the spliced portions of the web.
It appears that such thickly coated portion can occur not only in portions close to the aforesaid spliced portion of the web but also in those portions in the vicinity of discontinuities such as projections or ridges on the web surface, if so present, and coat-start portions and side end portions of the film (hereinafter referred to as "lugs" as a shorthand form of identifying the lateral edge portons of the web). The thickly coated amount in these areas is about 200 to about 250% of the normal coating amount in the vicinity of the splice portion, about 150 to about 300% in the coat-start portion, and about 120 to about 200% in the lugs. Even with an efficient coating operation, the lugs often extend about 3 to about 7 mm in from each side of the web (in the lateral direction), the coat-start portion (or coating start up portion) is about 5 to 20 mm along the travelling direction of the web and at the splices about 5 to about 20 mm along the travelling direction of the web will be thickly coated. As one skilled in the art will appreciate, normal coating amounts vary widely depending upon the kind of emulsion involved, and, therefore, there is no unequivocal definiation for the normal coating amount. Quite often, however, on commercial scale, normal coating amounts re less than about 40 .mu. in the dry state and about 5 to about 400 .mu. in the wet state.
Such thickly coated areas require much more time to dry than is required for drying normal areas, and, in the event that the drying is not sufficient, such thickly coated areas reach the humidifying step without being dried, and undried coating liquids are transferred to rollers or the like to contaminate the same and to harm films properly coated, resulting in product defects.
In the past, therefore, drying equipment has been provided, which is sufficient to dry the thickly coated areas, to avoid the defects noted above. However, such thickly coated areas do not yield acceptable finished products and will be thrown away, and, thus, the device for drying these thickly coated areas could be inherently be dispensed with. Moreover, usually the room required for the drying equipment which is used to dry these thickly coated areas occupies 30 to 50% of the entire production facility, thus, posing an uneconomical problem in terms of space utilization. Further, recent trends towards higher production tend to increase coating speeds; one way to accomplish this is to decrease the drying load involved, but there is a limit as to how far one can decrease the amount of coated material or increase the coating solution viscosity in order to decrease the drying load in order to decrease the amount of moisture which is to be removed by evaporation. Hence, the space occupied by drying equipment tends to inevitably increase, and, as a consequence, the aforesaid disadvantages become more pronounced.